Electron multiplier with multiplying path wall means having a reduced reducible metal compound constituent



Sept. 12, 1967 w ELECTRON MULTIPLIER WI A REDUCED REDUCI .GOODRICH ETAL 3,341,730

TH MULTIPLYING PATH WALL MEANS HAVING BLE METAL COMPOUND CONSTITUENT Original Filed June 16, 1961 INVENTORS GEORGE w.Go00mcH JAMES RIGNAUOWSKI ATTORNE United States Patent 23 Claims. (Cl. 313103) This invention pertains to an electron multiplier using secondary electron emission and arrays of such electron multipliers. The arrays have individual channels or tubes formed in accordance with the principles of Patent No. 3,128,408 entitled Electron Multiplier, issued Apr. 7, 1964 to Goodrich and Wiley. This application is a continuation of our earlier filed copending application Ser. No. 117,651 filed June 16, 1961, now abandoned.

In the Goodrich and Wiley patent, an image intensifier or channel multiplier is disclosed wherein a tube or channel of relatively small dimension, in the order of .001 inch diameter, is provided on the inside surface with a secondary emissive resistive material. A voltage differential is placed across each tube or channel to accelerate incoming electrons through the channel and also to supply current in the resistive coating for supplying the electrons that are used in the secondary emission. An array of many of these tubes, placed together, forms a multiplier section which may be used in an image intensifier or electron multiplier.

This invention provides a construction of an array of such multipliers disclosed in the Goodrich and Wiley patent. In the array of this invention, many glass tubes are fused together on the outside without distorting the inner surfaces or inner resistive surfaces of the tubes. This is accomplished by making each channel or tube with a plurality of layers so that the outer layer has a lower fusing temperature than the inner layer and therefore can be fused to other tubes without distorting the inner layers. The innermost layer of each tube is provided so that it has optimum secondary emissive and resistive properties.

It is therefore an object of this invention to provide an array of multiplier tubes which have a diameter of very small proportions, in the order of .001 inch, and with each tube having multiple layers with the outer layer being adapted for fusing to the outer layers of other tubes and having a fusing temperature lower than inner layers of the tube with the innermost layer of each tube having secondary emissive resistive properties. The temperature coefficients of expansion of the layers in each tube should be matched so that minimum strain is produced on temperature variation.

It is an object of this invention to provide such a tube having three layers, the outermost layer being of a low fusing temperature glass, a central or body layer, and an inner layer comprising a coating of glass having lead and bismuth to provide a resistive secondary emissive surface.

It is an object of this invention to provide an image intensifier array wherein each tube or channel has two layers, the outer layer being of glass having a low fusing temperature and an inner layer of glass having lead and bismuth compounds added to provide the proper conductivity, which layer is reduced to provide a resistive, secondary emissive surface. The temperature coefficients of expansions of the tube layers are closely matched so there will be a minimum of strain during temperature variations.

A further object of this invention is to provide a surface Patented Sept. 12, 1967 having an optimum combination of secondary electron emissive and resistive qualities on the inner surface of a vitreous tube or channel of extremely small diameter, in order of .001 inch, by providing in the vitreous body of the tube or channel compounds of substances such as lead or bismuth which, when reduced by a process such as hydrogen reduction, will provide not only a resistive surface but a surface having secondary emissive properties for a high order of electron multiplication.

These and other objects and advantages of this invention will become more apparent when preferred embodiments are considered in detail in connection with the drawings in which:

FIGURE 1 is a sectioned view of a first preferred embodiment showing a cross-section of a single channel multiplier tube with three layers;

FIGURE 2. is a view in perspective of several of the channel multipliers fused together to form an array; and

FIGURE 3 is a cross-section of a single multiplier tube of this invention having two layers.

FIGURE 1 shows an embodiment of this invention having a tube 18 with an outer layer of low fusing temperature glass 20, such as solder glass, and commercially available, which is fused to a central or body layer 22 of soda lime glass or other insulating material, and an inner layer 24 of a lead bismuth glass which when reduced provides a secondary emissive resistive surface utilized in the multiplier of the aforementioned Goodrich and Wiley patent. The temperature coefficients of expansion of the three layers 20, 22 and 24 are carefully matched to minimize the strains of temperature varia tion. Such a tube can be manufactured by taking a relatively large diameter glass tube 22 and coating in conventional manner with a solder glass layer 20. Then lead bismuth glass, which has been ground to a fine powder, is mixed with a binder such as nitro cellulose, 'amyl acetates, acetone or alcohol, and poured inside of the glass tube 22. This tube is then heated while rotating the tube to evenly coat and fuse to the glass body 22 an inner secondary emissive resistive coating 24. After this process is completed, the tube is drawn to a very small diameter such as .001 of an inch and cut into the necessary lengths, such as .05 of an inch.

The lengths are then placed in a stack, see FIGURE 2, and heated to a low temperature which will fuse the outer coatings 24}, but which will not affect the shape of inner layers 22, 24. This will bond the tubes 18 together to provide the desired array.

After the array has been formed a conductive coating 26 may be put on the ends by painting with a conductive paint such as a gold or silver paint, or by vapor depositing the gold or silver deposit at a steep angle on the tube ends so that it will not coat an undue amount of the tube interiors. A lead '28 can then be placed on a front tube end and a lead 30 can be placed on the rear tube end, with a voltage source 32 being placed between the leads to place the voltage differential across the tubes. Since all of the tubes at each end are electrically connected by the conductive coatings 26, there will be the same voltage across the tube.

A second embodiment is shown in FIGURE 3 where each tube has only two layers, an outer layer 34 of solder glass and an inner layer 36 which is formed of a glass body containing sufficient compounds of lead and bismuth to provide the desired conductivity when the inner surface is reduced. Such reduction can be done by heating the tubes to 325 degrees centigrade to 500 degrees centigrade for 8 to 16 hours while flowing one liter per minute of pure hydrogen through the tubes. This can be done after the tubes have been drawn to their small diameter.

3 Although this invention has been disclosed and illustrated with reference to particular applications, the principles involved are susceptible of numerous other applications which will be apparent to persons skilled in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.

Having thus described our invention, we claim: 1. An electron multiplier for multiplying electrons by secondaiy electron emission comprising wall means having a surface defining a multiplying path having its longitudinal dimension substantially larger than it lateral dimension, the multiplying path being totally free of any electrode means for focussing electrons which would tend to reduce the number of electron impacts with the wall means, entrance means for receiving particles to be multiplied by secondary electron emission from the wall means surface, exit means for discharging the secondary emission particles from the multiplying path defined by said Wall means and said exit means being spaced from said entrance means by said longitudinal dimension, said wall means comprising an insulative body having a reducible metal compound constituent therein, the surface of said wall means comprising chemically reduced reducible metal compound constituents to provide a resistive surface capable of secondary electron emission for said electron multiplication. 2. The multiplier of claim 1 with means for producing an electrical current flow longitudinally in said Wall means to establish in the multiplying path an electric field having a component parallel to the Wall means in its longitudinal dimension, means for providing an evacuated environment for said multiplying path.

3. The multiplier of claim 1 with said wall means comprising a tube having a diameter in the order of .001". 4. The multiplier of claim 1 with said wall means comprising a plurality of tubes fixed in substantially parallel relationship to form an ary, the inner surface of each of said tubes being secondary electron emissive and resistive. 5. The multiplier of claim 4 with at least some of the tubes having a layer of insulative material therearound, said layer of insulative material having a fusing temperature lower than said tube material. 6. The multiplier of claim 1 with said wall means comprising a vitreous body having lead and bismuth constituents therein, the surface of said wall means comprising reduced lead constituents and reduced bismuth constituents to provide a resistive secondary electron emissive surface.

7. The multiplier of claim 1 with said entrance means being open so that incoming particles may be received from a plurality of sources,

said lateral dimension being in the order of .001 inch.

8. The multiplier of claim 1 with said Wall means defining a plurality of multiplying paths each having its longitudinal dimension substantially larger than its lateral dimension, and each multiplying path being defined by a secondary electron emissive resistive surface,

said plurality of paths being closely adjacent each other and substantially parallel to one another to form an array of multiplying paths with the entrance means of said multiplying paths forming an input face and the exit means forming an output face,

means for placing substantially all of the entrance means of the plurality of multiplying paths at a given potential and substantially all of the exit means of the plurality of multiplying paths at a second potential. 9. The multiplier of claim 8 with at least some of the secondary electron emissive resistive surfaces having a layer of insulative material therearound,

said layers of insulative material having a fusing temperature lower than said secondary electron emissive resistive surface.

10. The multiplier of claim 1 with said wall means comprising an inner layer having said surface comprising reduced reducible metal compound to make the surface a secondary electron emissive surface having a predetermined resistivity,

an outer supporting insulative layer covering and fused to the outer surface of said inner layer.

11. The multiplier of claim 1 with the wall means comprising a vitreous body having a chemically reducible metal compound therein,

the surface of said wall means comprising chemically reduced metal compounds to provide a resistive secondary electron emissive surface.

12. An electron multiplier array comprising a plurality of channel electron multiplying members,

the wall of each channel member comprising an innermost layer, a central layer, and an outermost layer with the central layer being between and contiguous with the innermost and outermost layers,

the innermost layer being of a secondary electron emissive and electrically resistive material,

the central layer being of an electrically non-conducting channel support material,

the outermost layer being of an electrically non-con ducting thermal sealing material having a fusing temperature lower than said fusing temperature of said central layer,

said outermost layer covering substantially all of the outer surface of said central layer,

said innermost layer of each of said channel members comprising at least one of a chemically reduced lead glass and a chemically reduced bismuth glass.

13. An electron multiplier array containing a plurality of channel electron multiplying members,

the wall of each channel member comprising an inner layer and an outer layer with the inner layer being contiguous with the outer layer,

the inner layer having a secondary electron emissive and electrically resistive surface,

the outer layer being of an electrically non-conducting thermal sealing material having a fusing temperature lower than said inner layer,

said outer layer covering substantially all of the outer surface of said inner layer,

and said inner layer of said tubular members compris ing at least one of a chemically reduced lead glass and a chemically reduced bismuth glass.

14. The method of forming an electron multiplier having a secondary electron emissive resistive surface comprising the steps of obtaining a plurality of insulative tubular channels each having a relatively small diameter and each having a longitudinal dimension substanitally larger than its diameter dimension, providing in each of the tubular channels an entrance for receiving electrons to be multiplied and an exit for emitting the multiplied electrons,

providing said insulative channels throughout with sufficient reducible metal compound constituents to effeet a secondary electron emissive resistive surface when reduced,

placing said tubular channels in a substantially parallel relationship in close proximity to each other, heating the insulative channels to a temperature sufficiently high to reduce the reducible metal compound constituents therein,

reducing the inner surface of each of the channels to produce a secondary electron emissive resistive surface on the interior channel surfaces.

15. The method of claim 14 with the step of coating each end of each channel with a conductive 7 material so that the coating contacts the secondary electron emissive resistive surface.

16. The method of claim 15 with the step of coating the ends of each channel comprising vapor depositing a conductive material at an angle relative said channel ends so that the secondary emissive resistive material is placed in electrical contact with said coatings.

17. The method of claim 14 having the step of forming each of said channels with a vitreous material having quantities of lead constituents and bismuth constituents therein.

18. The method of claim 17 having the steps of heating said vitreous channels to a temperature between 325 degrees centigrade and 500 degrees centigrade for 8 to 16 hours flowing 1 liter per minute of hydrogen through the channels.

19. The method of claim 14 having the steps of coating said channels with an insulative coating having a fusing temperature lower than said insulative channels,

heating said coated channels to a temperature high enough to fuse said coating but low enough to preclude distortion of said channels.

20. The method of claim 14 with the step of forming each of said channels with a vitreous material having throughout sufiicient lead constituents to effect a secondary electron emissive resistive surface when chemically reduced,

21. A method of claim 14 with the step of passing a reducing gas through the longitudinal dimension of each of said iheated channels for a period the tubular channels so placed in parallel relationship in close proximity to each other and drawing said channels to a greater length and smaller cross section.

23. The method of forming an electron multiplier having a secondary electron emissive resistive surface comprising the steps of obtaining an insulative tubular channel having a relatively small diameter in the order of .001 inch and having a longitudinal dimension substantially larger than its diameter dimension,

providing the tubular channel with an entrance for receiving electrons to be multiplied and an exit for emitting the multiplied electrons,

providing said insulative channel throughout with sufficient reducible metal compound constituents to effect a secondary electron emissive resistive surface when reduced,

heating the channel to a temperature sufficiently high to chemically reduce the constituents therein,

passing -a reducing gas through the longitudinal dimension of said heated channel for a period of time to chemically reduce the constituents therein and produce a secondary electron emissive resistive surface on the interior channel surface.

References Cited UNITED STATES PATENTS 2,588,920 3/1952 Green 117-229 2,717,946 9/1955 Peck 1l7-229 2,992,956 7/1961 Bazinet 15689 3,128,408 4/1964 Goodrich et a1 3 l3--103 JAMES W. LAWRENCE, Primary Examiner. R. JUDD, Assistant Examiner. 

1. AN ELECTRON MULTIPLIER FOR MULTIPLYING ELECTRONS BY SECONDARY ELECTRON EMISSION COMPRISING WALL MEANS HAVING A SURFACE DEFINING A MULTIPLYING PATH HAVING ITS LONGITUDINAL DIMENSION SUBSTANTIALLY LARGER THAN IT LATERAL DIMENSION, THE MULTIPLYING PATH BEING TOTALLY FREE OF ANY ELECTRODE MEANS FOR FOCUSSING ELECTRONS WHICH WOULD TEND TO REDUCE THE NUMBER OF ELECTRON IMPACTS WITH THE WALL MEANS, ENTRANCE MEANS FOR RECEIVING PARTICLES TO BE MULTIPLIED BY SECONDARY ELECTRON EMISSION FROM THE WALL MEANS SURFACE, EXIT MEANS FOR DISCHARGING THE SECONDARY EMISSION PARTICLES FROM THE MULTIPLYING PATH DEFINED BY SAID WALL MEANS AND SAID EXIT MEANS BEING SPACED FROM SAID ENTRANCE MEANS BY SAID LONGITUDINAL DIMENSION, SAID WALL MEANS COMPRISING AN INSULATIVE BODY HAVING A REDUCIBLE METAL COMPOUND CONSTITUENT THEREIN, THE SURFACE OF SAID WALL MEANS COMPRISING CHEMICALLY REDUCED REDUCIBLE METAL COMPOUND CONSTITUENTS TO PROVIDE A RESISTIVE SURFACE CAPABLE OF SECONDARY ELECTRON EMISSION FOR SAID ELECTRON MULTIPLICATION. 